Airlines

You should be aware of the different airports of the Paris region when
buying your air ticket. The main commercial airlines mostly connect to
either Charles-de-Gaulle or Orly
airport both of which are well connected by public transport to the
city center. Low-cost carriers may, as well to to the above airports,
sometimes alight at Beauvais airport which has a less
convenient connection to Paris.

Most intercontinental and many inter-European flights to Paris arrive
here. Connections to the city:

The recommended means of transport is the commuter train
RER. The ride to Paris takes around 30 minutes, trains leave at
least every 15 minutes. Operates between 5 a.m. and midnight.
Price: 8.10 euros one way.

The first stop in Paris will be
Gare du Nord, from where the train continues southward through
Paris. See
here for a map of the Paris Metro, CDG airport is on the upper
right corner.

Train stations for RER are Charles-de-Gaulle 1 (for terminals 1 and
3), and Charles-de-Gaulle 2 (for terminal 2). You have to take a free
shuttle bus (line 2) between the train station to terminal 1, the other
terminals are in walking distance from their respective train stations
(but you also can use a free shuttle bus if you prefer).
Note: there seems to exist a brand new shuttle train which replaces the shuttle bus, but I haven't tried it yet.

The Roissybus bus services serves all three terminal and
goes to Paris Opera from where you have further RER and metro
connections. Busses leave every 15 minutes in the day and every 20
minutes in the evening hours, the ride takes between 45 and 60
minutes. (Price: 8.50 euros one way).

Taxi: about 50 euros to the city center at daytime, more at night.
Taxis might be stuck in the traffic during rush hours.

This airport is mostly used for domestic flights but also for some
international connections, as well as some low-cost carriers (notably
Easyjet). The most important connections to the city are:

The recommended means of transport is by train. An automated
shuttle train called Orlyval connects Orly airport to the train
station Antony where you change to the commuter train RER
to Paris. This connection can be used between 6 a.m. and 11 p.m. The
ride takes about 30 minutes. Price: 9.10 euro one way.

The first
stop in Paris will be Cité Universitaire, from where the train
continues northward through Paris. See
here for a map of the Paris Metro, Orly airport is at the center
of the lower edge.

Orlybus: This bus goes to the Denfert-Rochereau train
station where you have access to the RER and metro network. Price:
6.00 euro one way.

Taxi: about 35 euros to the city center at daytime, more at night.
Taxis might be stuck in the traffic during rush hours.

This airport is served by some low-cost carriers, notably Ryanair. The
only public transport to Paris is a shuttle bus to Porte
Maillot at the west end of Paris where you have access to the
Paris RER and metro network.

There are high-speed train connections to major cities in France and some
of the neighboring countries. The french name for the high-speed train is
TGV, but sometimes other commercial names are used for international
lines. Notable international direct high speed connections include: